This is just one more conversion of 58/1.2 lens with James Lao adapter. “Surgery” was successful. James was very fast with adapter delivery and dyxum site had critically important information for that success. Thanks to all dyxumer for help .

I do not want to talk about standard conversion procedure because you can read nice threads of JemsLao, Pete Ganzel, Arkku, Shaocaholica etc…
I want to share with you one small tip how to drill eight holes in adapter (yes eight (8) not four (4) as usual solution because that, more holes is better for more precious aligning axis of lens with axis of adapter –adapter does not have other possibility for correct line up with lens).

All explanations talk about drilling holes in adapter like something easy as 1, 2, 3…

Yes, it is easy for Pete Ganzel because he has workshop at home and bunch of nice machines to do all job properly , but at my computer table it was real challenge for me.

I've decided to use original mount of lens as pattern to drill holes in adapter. It's very important to align axes of adapter and axes of original mount before drilling holes.
It looks easy, but inner diameter of James adapter is a little larger than original lens mount. So, I did it with Scotch tape (but completely different using of Scotch tape )
First, I put adapter on Scotch tape (removed layer by layer to get stiff connection). After that I made cut around Scotch tape and removed layer by layer and at the end put original lens mount on tape.

Finally, lens mount and adapter are in proper position with aligned axes and you can drill eight holes (you have to mark start hole comparing by the one screw hole on the lens).

Please see the photos of that tip:

I spent about three hours to precisely drill holes and to assemble adapter with lens, but I spent even more to set infinity focus. I used Arkku's guide to set infinity focus but it was not enough and at the end I had to decrease thickens of the plate between adapter and lens from 4.1mm to 3.5mm. I've checked infinity focus at 3.9, 3.7 and finally at 3.5mm I've got infinity focus aligned with mark on the barrel of the lens.

This series of shots of orange building is not a “scientific” test, because these shots are made hand held through the closed window (distortion of doubled window glasses is visible…), but it was good test for my work and infinity focus. It seems I did it

All photos are made with A100 at ISO 100 (owners of A900 can shot at ISO 900 but I can not it is too noisy…) and without PP (JPEGS straight from camera resized only…)

F 1.2 +1 EV 1/1250 (a little blurred, maybe I was inpatient because I had very little time for this series )

The MD 50mm f/1.2 does not have a mount spacer ring like the 58mm lenses so the mount has to be a little more than a millimeter thinner. I'm not sure how others would do it but if you know a machinist or have access to a lathe, a standard T mount can be easily modified for a nice conversion;

Conversion to M42 is possible too with either lens but on the 50mm there is some destructive reduction of thickness needed on the lens itself.

Hi-jacking the thread a bit too... Pete, is that t-mount conversion reversible back to MD spec? It sure looks like a simple way to convert the lens. Also would a similar method work using a salvaged ex AF mount?

There is nothing, absolutely nothing, half so much worth doing, as simply messing about in boats

I have seen conversions done with the 58mm lenses and salvaged mounts (or M42 adapters as shown on this thread), where the spacer ring is sanded down to reduce the flange distance. I don't do it this way. With the 50mm there is no way to provide the little mating lip for the aperture ring because it is an integral part of the mount assembly. From the drawing you need around 4mm of thickness at the edge, which M42 adapters or salvaged mounts don't have. With the conversion to AF mount, you can just put the old mount back on since you are not modding anything on the old mount or lens itself

5/64ths is drill size I use. Disassemble the linkages inside the old mount so you can tape it tightly to the machined mount for drilling. Mark the tops of both before you do this and line them up. Again, PM me when you have it ready as there is an easy way with the 50mm to fine tune the infinity focus without disassembling the lens.

Ive decided to keep an eye out for a 58mm. I have compared some old photos I have taken with the 50mmF1.2 and the photos krca has shown here (and many others on the web). It appears to me the 58mm edges out the 50mm on bokeh and overall seems to produce a slightly nicer focus on the subject. Can 8mm in focal length effect really affect the photo much?
(Then again could just be the photographer )

If I cant find a 58mm then I will attempt a 50mm conversion (my dads a fitter and machinist).

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